A review of literature about psychic illness in migrant workers (with special reference to the situation in Europe) is presented, including the problems of incidence and prevalence, course of the illness, typical syndromes and treatment. Results concerning incidence and prevalence of psychic disease in migrant workers are contradictory and partly--for methodological reasons--of questionable quality. It cannot be take for granted, that migrant workers suffer more often from psychiatric disturbances than either of the two possible control groups: the populations of the emigration or immigration countries respectively. There are two high risk periods for migrants: shortly after the migration and after a longer period in the guest country. Differences between the migrant's culture and that of the immigration context (language, mythical beliefs, illness behavior) influence the manifestations of psychiatric syndromes. The following syndromes are typical for migrant workers: paranoid reactions, hypochondric-depressive syndromes, psychosomatic conditions and sexual neurosis. Special attention requests the treatment of migrant workers with psychiatric problems; the aspects of psychotherapy, accompanying social measures and the return as therapeutic measure are discussed. In the second part, a general frame of reference for the sociological analysis of the problem of migrant workers is presented. Reasons for the mass immigration of foreign workers to the industrialized countries of central Europe were the demand of labor force and the large gap in socio-economic development between the countries. In the immigration context, the foreign workers find themselves in the lowest social strata and numerous problems accumulate there. Empirical evidence for different sociological explanations of mental illnes of migrant workers ist presented: hypotheses of social selection vs. social causation (low socio-economic status, goal-striving-stress, culture-shock theory, theory of culture change and isolation hypothesis).